The researchers deep fried and pan-fried raw potato pieces in four different refined oils - olive, corn, soybean and sunflower and reused the oil 10 times.

They found that olive oil was the most stable oil for deep-frying at 320 and 374 degrees Fahrenheit, while sunflower oil degraded the fastest when pan-fried at 356 degrees Fahrenheit.

"For frying foods, olive oil maintains quality and nutrition better than seed oils," said lead researcher Mohamed Bouaziz. Different oils have a range of physical, chemical and nutritional properties that can degrade when heated.

Some of these changes can lead to the formation of new compounds that are potentially toxic.

By-products of heating oil can also lower the nutritional value of the food being fried.

The study was reported in ACS' Journal of Agricultural and Food Chemistry.